The GM signs were "Code" in the U.S. but not the U.K. I have had to open a wall enough times ( once ) and reconnect EMT to know why the British require that there be a redundant grounding conductor in metal conduits in all occupancies and not just in hospitals like in the U.S.

On almost all commercial wiring jobs here in Ohio a redundant grounding conductor for metal conduit is a job specification. Most customers like grounded.

Oh yeah, the experience of the amateur radio community is that the anchor bolts and reinforcing rods in a tower footer need to be bonded to each other and to an adjacent ground rod so that lightning does not blow up the footer.

However, my experience with ungrounded 480 volt systems and ther telephone company experience is that there is also a lot of damage from low energy lightning or even invisible lightning such as Saint Elmo's Fire. This is mostly a trickle of direct current from cloud to ground and well as electrostatic induction. Therefore, a sign or tower does need a reasonable local ground against the flow of direct current.

Just remember that even for the high frequency components of lightning a local ground will usually have lower inductance than the equipment grounding conductor.

Mike Cole

Mike Cole